It's not intuitive to me how big of a difference 4.5 Hz is, but you really need to use a logarithmic scale (because, for instance, shifting everything up an octave will yield different errors in Hz). In cents, that's about a 16 cent difference, while an equal tempered semitone is 100 cents. Is 16 cents easily noticeable? I don't have a nice tuner handy, so I can't say.
Still, your claim doesn't seem right to me. A perfect tuned guitar with perfect intonation in equal temperament will play the same frequencies as a perfectly tuned piano. Yet, when I play G and E chords on a piano, I don't notice the same tuning issues as I often do on guitar. That's why I assumed the bigger issue on guitars is intonation.
Still, your claim doesn't seem right to me. A perfect tuned guitar with perfect intonation in equal temperament will play the same frequencies as a perfectly tuned piano. Yet, when I play G and E chords on a piano, I don't notice the same tuning issues as I often do on guitar. That's why I assumed the bigger issue on guitars is intonation.